Processes for producing an optically active L-α-amino acid by contacting a microorganism or a microbial enzyme with an α-amino acid amide are known (JP Patent Publication (Kokai) Nos. 59-159789 (1984), 61-119199 (1986), 62-55097 (1987), 1-277499 (1989) and 5-30992 (1993)). Each of these methods uses a reaction mediated by a microbial amide hydrolase. The amide hydrolase, also called amidase, catalyzes the hydrolysis reaction of an acid amide group into a carboxylic acid and an amine or ammonia. The microbial amide hydrolase is characterized in that it stereoselectively hydrolyzes an α-amino acid amide to produce an optically active L-α-amino acid. The term “optically active L-α-amino acid” refers to an amino acid containing a levorotatory enantiomer in a larger amount than the other enantiomer, or an amino acid consisting of a levorotatory enantiomer alone.
However, when a microorganism or microbial enzyme is industrially used for producing a substance; the stability and activity of the amide hydrolase used must be sufficiently high in view of cost performance. Since all microorganisms used in the aforementioned methods are mesophilic bacteria, which cannot proliferate at a temperature of 55° C. or higher, the amide hydrolases derived from these microorganisms are low in stability in the range of ordinary temperature or higher. Therefore, when a reaction takes place at high temperature, the problem that the reaction slows down or stops occurred because the enzyme becomes unstable.